Worldwide Pollution Control Association

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1 Worldwide Pollution Control Association Michigan Coal to Gas Seminar June 5-6, 2012 All presentations posted on this website are copyrighted by the Worldwide Pollution Control Association (WPCA). Any unauthorized downloading, attempts to modify or to incorporate into other presentations, link to other websites, or to obtain copies for any other purposes than the training of attendees to WPCA Conferences is expressly prohibited, unless approved in writing by the WPCA or the original presenter. The WPCA does not assume any liability for the accuracy or contents of any materials contained in this library which were presented and/or created by persons who were not employees of the WPCA. Visit our website at

2 SCR/CO Catalyst Considerations WPCA/Gulf Power Coal to Gas Conversion Seminar Detroit, FL June 5-6, 2012 Ken Jeffers

3 Topics Regulatory Drivers for Controlling Emissions NO x, CO SCR Catalyst for NO x control CO oxidation catalyst

4 Regulatory Drivers - NO x Control NO 2 is 1 of 6 criteria pollutants Respiratory irritant, contributes to low-level ozone formation Regulated per EPA NAAQS MATS, Amendments to NSPS: NO x emission limit 0.7 lb/mwh Further controls necessary per CSAPR which requires: 23 states to reduce SO 2 and NO x to help downwind states attain hour and/or 1997 annual PM 2.5 NAAQS 20 states to reduce Ozone Season NO x to help downwind areas attain hour Ozone NAAQS

5 CSAPR States

6 Regulatory Drivers - CO Control CO is 1 of 6 criteria pollutants Majority of CO emissions come from mobile sources CO displaces oxygen to the heart and brain Contributes to low-level Ozone formation CO + 2O 2 CO 2 + O 3 NAAQS for CO 8-hour average: </= 9 ppmv 1-hour average: </=35 ppmv

7 Fossil Fuel Air Emissions Comparison (lb/mmbtu of Energy Input) Pollutant Natural Gas Oil Coal Carbon Dioxide Carbon Monoxide (?) Nitrogen Oxides Sulfur Dioxide Particulates Mercury x x 10-3

8 SCR Catalyst for NO x Control

9 SCR Configuration with Coal-fired Boilers High Dust Source: The Babcock and Wilcox Company

10 SCR Configuration with Coal-fired Boilers Low Dust Hot-Side ESP Air Preheater

11 SCR Catalyst Types Plate Honeycomb Corrugated

12 Plate-type Catalyst Composition Stainless steel expanded mesh substrate, coated with ceramic material TiO 2, V-oxide/W-oxide/Mo-oxide Notches formed into plates provide separation Inserted in element boxes with variable spacing: 60 to 90 plates Variable plate height up to 700 mm Advantages Ideal for high dust configurations Plugging, erosion resistance Low pressure loss

13 Honeycomb Catalyst Composition Homogeneously extruded ceramic with square-opening cell structure TiO 2, V-oxide/W-oxide Variable block height up to 1300 mm Pitch: 2.1 mm 9.2 mm Advantages Ideal for low/no-dust applications High active surface area per unit volume

14 Catalyst Pitch and Structure Pitch = center to center distance from one plate/wall to the next pitch pitch Plate-Type Structure Flexible plates Rectangular openings Pitch: 5 to 7 mm Honeycomb Structure Rigid structure Square openings Pitch: 2.1 to 9.2 mm

15 Pitch Selection by Application Application Plate Pitch Honeycomb Pitch Natural Gas, Diesel mm (70 x 70 cell) 3.7 mm (40 x 40 cell) Tail-End, Low-dust Fuel Oil Bituminous Coal PRB Coal mm mm mm mm 3.7 mm (40 x 40 cell) 6.7 mm (22 x 22 cell) 4.9 mm (30 x 30 cell) 6.4 mm (23 x 23 cell) 6.7 mm (22 x 22 cell) 8.2 mm (18 x 18 cell) 8.2 mm (18 x 18 cell) 9.2 mm (16 x 16 cell) Lignite mm? (no US examples)

16 Catalyst Modules for Utility SCRs Catalyst elements arranged in steel frames Plate 2 levels of 8 element boxes Honeycomb 72 monoliths Standardized cross-section Possible to interchange catalyst types within reactor Module height varies with catalyst height

17 Suitable Operating Conditions Flue Gas Temperature: F Flue gas linear flow velocity: m/s Thorough NH 3 -NO x mixing: 5% RMS (required for >85% denox with low NH 3 slip) For flue gas with particulate matter, need Popcorn ash/lpa screens upstream of SCR reactor Soot-blowers or sonic horns at catalyst layers Means to keep catalyst dry and frost-free during outage periods

18 SCR Catalyst Deactivation Relative Activity/Potential NG Bituminous Coal PRB Coal Biomass Operating Time

19 Catalyst Deactivation Mechanisms Masking: Macroscopic blockage of catalyst surface by cemented fly ash Cemented Fly Ash Catalyst Surface Pore System Plugging: Microsopic blockage of pore system by small fly ash particles Catalyst Surface Pore System Small Fly Ash Particles Poisoning: Deactivation of active sites by chemical attack Catalyst Surface Pore Active Sites System

20 Advantages with Gas-firing Catalyst Selection For Coal... Large pitch to avoid ash plugging Minimized SO 2 -SO 3 oxidation Frequent replacement every 2 years For Natural Gas firing... Much slower catalyst deactivation longer catalyst life Fewer catalyst replacements No fly ash plugging No Sulfur no ABS, can tolerate higher NH 3 slip Possible reduced NO x reduction requirements If 100% gas, can use higher cell density catalyst reduced volume requirement

21 Sizing Examples Base Bit Coal Case NG equal NO x load NG reduced NO x load NO x in 300 ppmvd 300 ppmvd 240 ppmvd NO x out 40 ppmvd 40 ppmvd 40 ppmvd NO x Reduction 87% 87% 83% NH 3 slip 2 ppmvd 2 ppmvd 5 ppmvd Rel P Catalyst Pitch 5.6 mm plate 3.7 mm HC 3.7 mm HC Relative Volume Pressure drop 1.7 iwg 1.9 iwg 1.5 iwg

22 Catalyst Options for Coal to Gas Conversion For Units already having SCR with coal-fired catalyst Conversion to 100% Gas firing is OK Remove portion of coal-fired catalyst for reuse in other coal units Replace all coal-fired catalyst with gas-fired catalyst If coal will be backup fuel or co-fired, gas-specific catalyst is not suitable Fly ash plugging High SO 2 SO 3 oxidation If SCR required on unit after conversion Conversion to 100% Gas firing install gas-fired catalyst Conversion to Gas with Coal backup or co-firing gas and coal need catalyst suitable for coal-firing.

23 CO Oxidation Catalyst Oxidizes CO and VOCs to CO 2 Stainless steel foil or ceramic honeycomb substrate, high surface area alumina washcoat, Platinum Group Metals (PGM) embedded in washcoat Blocks with 25 cpsi 400 cpsi Standard block is 24 x 24, 200 cpsi metal foil for gas turbine applications Variable block cross-section possible Metal foil depths of inches

24 Catalyst Conversion Efficiency Catalyst conversion efficiency depends on catalyst durability, reactant residence time and the active surface area of the catalyst Active Sites Washcoat Substrate Catalyst activity maximized by dispersing the active metals throughout the high surface-area washcoat on the substrate media

25 Catalyst Light-Off Temperature range at which conversion occurs

26 CO Oxidation Catalyst Performance Fuels Suitable for NG or ULSD CO Reduction % Range 80-90% Typical VOC Reduction 0 70% Range 0 50% Typical Pressure Drop 1.0 iwg Typical Performance Guarantee Period 3 years or 5 years Typical

27 Oxidation Catalyst Placement CCGT HRSG Example

28 Oxidation Catalyst Placement in a Boiler Possible CO catalyst location upstream from NH 3 injection for SCR Source: The Babcock and Wilcox Company

29 Catalyst Deactivation Mechanisms Thermal deactivation: (typically irreversible) Occurs above 1200 F Failure of substrate material Sintering of active catalytic species Sintering of support Reaction of catalyst materials Catastrophic thermal event Poisoning: (typically reversible) Chemical (selective) contamination of active sites Physical (non-selective) contamination masking, fouling, plugging of cells/pores, washcoat attrition

30 Catalyst Deactivators (Poisons) Heavy and Base Metals: - Lead (Pb) - Iron (Fe) - Arsenic (As) - Chrome (Cr) - Zinc (Zn) - Phosphorous (P) - Copper (Cu) - Silicon (Si) - Sulfur (S) - Nickel (Ni) - Mercury (Hg) - Antimony (Sb) -Tin(Sn) High Molecular Weight Organic Material Dust and Particulates CO Catalyst NOT SUITABLE FOR COAL-FIRED APPLICATIONS

31 Selective (Chemical) Poisoning Example Sulfur can react directly with active site and degrade performance. Pt + S PtS alloy Alloy has low activity (For certain poisons it is possible to reactivate the catalyst by thermal treatment)

32 Catalyst Regeneration or Cleaning Options Thermal Elevating Temperature Oxidizes organic material Physical Vacuuming or Compressed Air Blowing Removes dust and debris Chemical (including DI Water) Washing Removes masking agents Restores surface area Reduces poison concentration

33 CO Catalyst Options if required after Coal to Gas Conversion Suitable for units converted to 100% Gas firing Not suitable for coal firing (or fuels containing particulate and Sulfur) Back-up fuel or co-firing Suitable for low S fuel oil / ULSD / Light oil (?) used as back-up fuel. Firing should be limited Typically < 500 hours per year Not suitable for HFO

34 Summary Points Gas-firing has many advantages for SCR Slower deactivation longer lifetime Low/No Sulfur No ABS, higher NH 3 slip tolerable No fly ash/particulate plugging May result in Lower NO x load, lower denox requirement Low pitch, high cell density catalyst elements lower volume requirement as compared to coal applications Catalyst sized for natural gas not suitable for coal-firing CO Oxidation catalyst suitable for gas-firing and low/no sulfur fuels High rates of CO oxidation are possible CO Oxidation catalyst is not suitable for coal-firing or fuels with ash/particulate

35 Thank You! Ken Jeffers Sr. Applications Engineer